Nickel allergy is one of the most common types of contact allergies. In Europe about 10% of all women suffer from this type of allergy while being less frequent in the male population. It is an important occupational disease but due to the widespread use of nickel-containing products it is a significant problem among people in general. The difference between the sexes is partially explained by the more common use of jewellery among women and quite often ear piercing seems to be the event that induces the disease. Nickel allergy is usually life-long and there is presently no, effective treatment apart from avoiding exposure.
Unlike many other allergies (e.g. against animals, pollen, plants, etc.), contact allergies are usually not associated with a rise in allergen specific IgE antibodies. As the diagnosis of allergy in vitro is normally based on the detection of specific IgE in serum there is presently a lack of suitable serological tests for nickel allergy. The most commonly used method for establishing nickel allergy is based on the so called patch test in which nickel is introduced into the skin of the patient and, depending on the presence or absence of a local inflammation, the patent is diagnosed as being allergic or non-allergic. The measured size of the inflammatory site may also serve as an indicator of the severity of the allergy. A major drawback of the patch test, apart from the discomfort that it may cause the individual, is the risk that the exposure to nickel during the test in itself may induce or enhance the disease. The test may also give false positive or false negative responses and the capacity to respond may be affected by the hormonal status of the individual as well as by certain drugs and by uv-light.
Attempts have been made to measure the specific activation of cells after in vitro exposure with nickel. This has been done by measuring cell proliferation or the release of cytokines by the stimulated cells. However, given the low frequency of nickel-specific cells in peripheral blood, cell proliferation has often proven too insensitive and unreliable and the detection of nickel-induced cytokine production by ELISA usually requires the propagation and in vitro culturing of cells to first expand the population of responding cells. Furthermore, as shown from analysis of nickel-specific T cell clones, cytokine production is heterogenous and no single cytokine has been shown to be consistently produced by the responding cells.